/*
 * Copyright 2002-2017 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.reactive.function.server;

import org.springframework.core.io.Resource;
import org.springframework.http.HttpMethod;
import org.springframework.http.HttpStatus;
import org.springframework.lang.Nullable;
import org.springframework.web.reactive.function.BodyInserters;
import reactor.core.publisher.Mono;

import java.io.ByteArrayInputStream;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.net.URI;
import java.net.URL;
import java.util.EnumSet;
import java.util.Set;

/**
 * Resource-based implementation of {@link HandlerFunction}.
 *
 * @author Arjen Poutsma
 * @since 5.0
 */
class ResourceHandlerFunction implements HandlerFunction<ServerResponse> {

    private static final Set<HttpMethod> SUPPORTED_METHODS =
            EnumSet.of(HttpMethod.GET, HttpMethod.HEAD, HttpMethod.OPTIONS);


    private final Resource resource;


    public ResourceHandlerFunction(Resource resource) {
        this.resource = resource;
    }


    @Override
    public Mono<ServerResponse> handle(ServerRequest request) {
        HttpMethod method = request.method();
        if (method != null) {
            switch (method) {
                case GET:
                    return EntityResponse.fromObject(this.resource).build()
                            .map(response -> response);
                case HEAD:
                    Resource headResource = new HeadMethodResource(this.resource);
                    return EntityResponse.fromObject(headResource).build()
                            .map(response -> response);
                case OPTIONS:
                    return ServerResponse.ok()
                            .allow(SUPPORTED_METHODS)
                            .body(BodyInserters.empty());
            }
        }
        return ServerResponse.status(HttpStatus.METHOD_NOT_ALLOWED)
                .allow(SUPPORTED_METHODS)
                .body(BodyInserters.empty());
    }


    private static class HeadMethodResource implements Resource {

        private static final byte[] EMPTY = new byte[0];

        private final Resource delegate;

        public HeadMethodResource(Resource delegate) {
            this.delegate = delegate;
        }

        @Override
        public InputStream getInputStream() throws IOException {
            return new ByteArrayInputStream(EMPTY);
        }

        // delegation

        @Override
        public boolean exists() {
            return this.delegate.exists();
        }

        @Override
        public URL getURL() throws IOException {
            return this.delegate.getURL();
        }

        @Override
        public URI getURI() throws IOException {
            return this.delegate.getURI();
        }

        @Override
        public File getFile() throws IOException {
            return this.delegate.getFile();
        }

        @Override
        public long contentLength() throws IOException {
            return this.delegate.contentLength();
        }

        @Override
        public long lastModified() throws IOException {
            return this.delegate.lastModified();
        }

        @Override
        public Resource createRelative(String relativePath) throws IOException {
            return this.delegate.createRelative(relativePath);
        }

        @Override
        @Nullable
        public String getFilename() {
            return this.delegate.getFilename();
        }

        @Override
        public String getDescription() {
            return this.delegate.getDescription();
        }
    }

}
